A technique of photo-curing of a liquid resin, and the like (a technique of polymerization and curing by irradiation of an active energy ray such as ultraviolet rays) takes advantage of characteristics such as curing at a low temperature, shortening of processes, short time curing and excellent fine workability as compared to conventional thermosetting techniques, and has been widely used for an adhesive agent, a sealing agent, a coating agent, a resist agent, and the like. Curing systems that are generally used in photo-curing at present are roughly divided into the radical curing system and the cation curing system. In the case of the radical curing system, a photoradical generating agent and a (meth)acrylate resin are main components, the system has a characteristic of quickly curing after light irradiation but has problems such as having generally low adhesion strength, large curing contraction and poor heat resistance. On the other hand, the cation curing system is constituted of a photo-acid forming agent such as diaryl iodonium salt and a triaryl sulfonium salt, and an epoxy resin, an oxetane resin, a vinyl ether resin, or the like, which has a cation polymerization property, and the photo-acid forming agent generates an acid in light irradiation to make a cation polymerizable resin cured. In the case of cation curing, the system has characteristics such as quick curing property, high adhesion strength and low curing contraction, but has problems such as generating curing defect due to moisture or a subtle basic stain in the surface of an adherent and causing erosion when the system is used for an adherent made of a metal or an inorganic material since a strong acid remains in the system.
As one means for solving such problems of the cation curing system, a study of anion curing by a photobase generating agent that generates a basic compound by light irradiation has been made in recent years. As such a photobase generating agent, for example, a carbamate derivative and an oxime ester derivative have been generally known, these compounds generate primary or secondary amines by light irradiation and used for curing of an epoxy resin (Non-Patent Literature 1). A technique of generating a basic compound by light has been largely used for a photoresist technique and, in order to obtain size stability of an edge developed in a narrow line width resist, an anion polymerization type curing system having less termination reactions is largely used (Non-Patent Literature 2 and Patent Literatures 1, 2 and 3). In a technique of curing an epoxy resin by a basic compound generated by light, examples of typical basic compounds include amines, and amines are bases generated by light, which have been the most useful until today. For example, a substituted benzyl carbamate derivative generates primary and secondary amines by light irradiation, which enables a curing reaction of an epoxy compound (Non-Patent Literatures 3, 4 and 5). On the other hand, trials for photochemically generating tertiary amines have been studied. Photo decomposition of a tetraalkyl ammonium salt is proposed as a method of photochemically generating tertiary amine (Non-Patent Literature 6).
Patent Literature 5 discloses a carboxylic acid ammonium salt, Patent Literature 6 discloses an α-aminoacetophenone derivative, Patent Literature 7 discloses an aromatic amineimide compound, Patent Literature 8 discloses a composition containing an amineimide compound, singlet•triplet sensitizing agents, and an epoxy resin. Further, Patent Literature 9 reports a system in which α-aminoacetophenones are present as a compound that effectively generates tertiary amine, and tertiary amine is more effectively generated after light irradiation in an addition curing reaction of an epoxy resin obtained by combining the compound and a hydrogen-drawing type radical initiator reacted with polyvalent thiol compounds to thus cure a resin. What is more, Patent Literature 10 and Non-Patent Literature 7 report curing of an epoxy resin by a compound that generates amidines by light, and a composition made of an epoxy resin and a thiol compound. Other than these compounds, a salt compound of quaternary ammonium and tetraphenyl borate (Non-Patent Literature 8), a salt compound of triazabicyclodecene and tetraphenyl borate (Non-Patent Literature 9), and the like, were reported as a photobase generating agent.
As described above, there are a large number of reported examples of techniques of generating a basic compound by light and such techniques have very high usefulness as a polymerization (curing) initiation system in curing an epoxy resin, in particular. However, in a photobasic generation system that has been reported so far, particularly in a system of generating tertiary amine, the generation efficiency is not very high and the system has a defect such that light irradiation for a long time is necessary to sufficiently generate amines. In the inventions described in the Patent Literatures 5 and 6, generation efficiency of tertiary amine to be generated is high but the generated tertiary amine has a low ability of catalytic activity and does not make an epoxy resin cured.
On the other hand, systems described in Patent Literature 7, Patent Literature 8, Non-Patent Literature 8 and Non-Patent Literature 9 are considered to be more useful for generating tertiary amine, but in fact, a time until an epoxy resin reaches complete curing is very long and the systems do not attain giving sufficient photo-curability to the epoxy resin. Patent Literature 9 discloses a composition made of an epoxy resin, a thiol compound and a photoanionic initiator, but the composition also does not have an ability of curing an epoxy resin quickly after completion of light irradiation.
Patent Literature 10 and Patent Literature 11 disclose curing of an epoxy resin by a compound that generates amidines having a large basic property by light as a photoanionic initiator and a composition made of an epoxy resin and a thiol compound, but do not mention specific blending compositions and how much curing speed is shown. Non-Patent Literature 7 discloses a technique of curing a composition made of an epoxy resin, polythiol and the photoanionic initiator disclosed in Patent Literature 10 in 2.5 hours after energy ray irradiation and that an optical a of the composition is more improved by thioxanthone or benzophenone, but the technique does not have a curing speed at a degree capable of curing an epoxy resin quickly after completion of light irradiation and storage stability of the composition was not also sufficient.